A blast from the past...
Funnily enough, the 'screenplay question' also came up again very recently and I posted an updated option. See
this thread, my contribution starts at post #8.
This method involves creating a TXT file (containing all the formatting spaces) from the PDF using the XPDF (free) Windows utilities. Google should find it quickly.
Once you have the nicely formatted TXT it is simple to run a TXT-->epub conversion to get something which reads very nicely on a PRST1 in landscape orientation. The linked thread shows some pictures.
It all hinges on whether you can get the relevant XPDF commandline utility to run in your Mac-Windows environment.
If it works, the rest is easy, but if you get stuck with the necessary 'TXT Input' calibre conversion options, I can be more specific.
[Edit:] dear, oh dear I really should get my facts straight before posting
The TXT to epub calibre conversion does work, but I got a better result by dropping the TXT file into a boilerplate HTML file and doing a ZIP to epub conversion. Let me relook at my test files and I'll post further details later.